//
// detail/null_global.hpp
// ~~~~~~~~~~~~~~~~~~~~~~
//
// Copyright (c) 2003-2022 Christopher M. Kohlhoff (chris at kohlhoff dot com)
//
// Distributed under the Boost Software License, Version 1.0. (See accompanying
// file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
//

#ifndef ASIO_DETAIL_NULL_GLOBAL_HPP
#define ASIO_DETAIL_NULL_GLOBAL_HPP

#if defined(_MSC_VER) && (_MSC_VER >= 1200)
# pragma once
#endif // defined(_MSC_VER) && (_MSC_VER >= 1200)

#include "asio/detail/config.hpp"

#include "asio/detail/push_options.hpp"

namespace asio {
    namespace detail {

        template<typename T>
        struct null_global_impl {
            null_global_impl()
                    : ptr_(0) {
            }

            // Destructor automatically cleans up the global.
            ~null_global_impl() {
                delete ptr_;
            }

            static null_global_impl instance_;
            T *ptr_;
        };

        template<typename T>
        null_global_impl<T> null_global_impl<T>::instance_;

        template<typename T>
        T &null_global() {
            if (null_global_impl<T>::instance_.ptr_ == 0)
                null_global_impl<T>::instance_.ptr_ = new T;
            return *null_global_impl<T>::instance_.ptr_;
        }

    } // namespace detail
} // namespace asio

#include "asio/detail/pop_options.hpp"

#endif // ASIO_DETAIL_NULL_GLOBAL_HPP
